The present application relates generally to semiconductor devices and includes methods and structures for improving lithography.
An important capability for manufacturing reliable integrated circuits is to precisely shape the individual structures that form the integrated circuits. To form the individual structures, a patternable layer such as a photo resist is formed on another layer. The patternable layer is then patterned using a mask, for example by exposing only portions of the photo resist to a light source. The exposure to the light source alters the photo resist such that a selected portion of the photo resist may be removed providing the patterns that will shape the individual structures that will be formed.
FIG. 1A shows a mask that has an assist feature. The mask 10 provides for the main feature 12, which may correspond with a contact hole. An exemplary assist feature is shown as the scattering bars 14. The scattering bars 14 provide for an increased image contrast. In this example, the wider the scattering bars 14 the larger the process window (the window in which the depth of focus of the projected image is acceptable and the pattern size is within a designated specification). However, the more aggressive an assist feature is (i.e., the wider the scattering bars 14), the larger the problem of assist feature print out is. Referring to FIG. 1B, the patterned layer 20 includes the desired patterned features 22 and undesired assist feature print out 22.
It would be desirable to improve the lithography to reduce or eliminate the effect of assist feature print out.